1. Field of the invention
The present invention relates to a system and a method for recovering CTA (crude terephthalic acid) residues and for purifying and regenerating catalyst, being used in the technical field of the reaction process of oxidation in manufacturing PTA (purified terephthalic acid), and especially relates to a system and a method in which the mother liquid of the CTA generated is treated to form CTA residues and is recovered to make oxidized catalysts to be circulated for reusing.
2. Description of the Prior Art
A method of producing purified terephthalic acid (PTA) uses para-xylene (PX) as raw material to produce a kind of white powder of the purity of 99.95% through the reaction process of oxidation and hydrogenation (refining). PTA is one of the main raw materials for manufacturing polyester fiber for making polyester containers (such as PET bottles), plastic for engineering and plaster.
In a process of oxidation 20 for PTA, please refer to FIG. 1, it is mainly that air is blown into a reactor for oxidation to mix with the para-xylene (PX), catalysts and acetic acids (HAc), and to proceed to oxidation of the mixed solution under the pressure of 16.5 kg/cm2G and 204° C. to produce crude terephthalic acid (CTA). And in the process of oxidation 20, oxidized catalysts containing the ions of cobalt, manganese and bromine are wanted and added, and cobalt and manganese ions of two valences are used as catalysts, bromine ion is used as initiating agent. The main ingredients of oxidized catalysts used presently are compounded from three elements Co, Mn and Br, call shortly as a CMB oxidized catalyst.
And in a process of hydrogenation 30, crude terephthalic acid (CTA) is pulped and mixed, then hydrogen is added therein to react with palladium catalyst under high temperature and high pressure, 4-carboxyl benzaldehyde (4-CBA) impurity contained therein is reduced to water soluble p-toluic acid, and is produced to form PTA after centrifugation, water washing, filtering, separating and crystal drying.
Therefore, after oxidation of CTA, the process of hydrogenation 30 is required to refine the crude terephthalic acid (CTA) to form purified terephthalic acid (PTA); hence impurities in the process of manufacturing CTA shall be separated and discharged in advance, the impurities are called as CTA residues. The discharged CTA residues further are passed through a thin film evaporator system (TFE) to separate and recover the acetic acid (HAc) contained therein, then is passed through a pulping can (POT) which is added with water to lower the temperature and is discharged, the concentrations of the cobalt and manganese ions in the CTA residues obtained each is 0.1˜2 wt%; the present invention aims at taking and recovering the heavy metals in the CTA residues.
Related prior art such as the U.S. Pat. No. 3,341,470 collects catalyst by the method of incineration, and U.S. Pat. No. 6,001,763 uses electric arc or electric torch of the field of electricity or plasma to produce catalysts of metallic power etc.; these are all energy consumptive manufacturing processes, and wherein the process for manufacturing terephthalic acid react under high temperatures and in acids, this makes the metallic alloys (Fe, Ni, Zn, Cr, Cu and Pb etc.) contaminated in the reaction instruments unable to be separated.
Catalyst recovering methods available presently are all chemical methods, they are recovering methods unable to separate the discharged catalysts and the impurities, such as those catalysts recovered by conventional recovering methods in the process of oxidation, this may induce accumulation of impurities during circulation. Thereby these conventional recovering methods are required to be improved.